I wouldn't bother. You will get the benefits of a VTEC head but you won't get the all the advantages a stock VTEC version of your car would have and you will be slower. A factory VTEC engine is going to have slightly higher compression pistons and a more agressively geared tranny, two things you can swap over but for the same cost, could probably just do a complete Z6 engine swap (tranny and all). If you want to stick with a SOHC engine, that's what I would do. Find a complete D16Z6 from a '92-'95 EX coupe or sedan or Si hatch and swap that into your car. I believe your current mods will swap right over (specifically the header and intake) and if you search around and find a solid motor and install a new timing belt, water pump, some new hoses and do a good tune up you should have a solid running engine that will be very reliable. I don't know how comfortable you are with working on your car but rigging together a new engine from a few other engines usually isn't as reliable as letting the factory do it. Seeya.